Natural accommodation in a normal human eye having a normal human crystalline lens involves automatic contraction or constriction and relaxation of the ciliary muscle of the eye (and zonules controlled by the ciliary muscle) by the brain in response to looking at objects at different distances. Ciliary muscle relaxation, which is the normal state of the muscle, shapes the human crystalline lens for distant vision. Ciliary muscle contraction shapes the human crystalline lens for near vision. The brain-induced change from distant vision to near vision is referred to as accommodation.
Accommodating intraocular lens (IOL) assemblies have been developed that comprise an IOL that moves in response to ciliary muscular contraction and relaxation, thereby to simulate the movement of the natural lens in the eye, and, inter alia, help provide patients with better focusing ability.
One example of an accommodating IOL assembly is described in U.S. Pat. No. 5,476,514 to Cumming. Cumming describes an accommodating IOL with plate haptics for implantation within the capsular bag of the eye, after removal of the natural lens by an anterior capsulotomy. During a postoperative healing period following surgery, anterior capsular remnants fuse to the posterior capsule of the bag by fibrosis about the plate haptics, and the lens is deflected rearward to a distant vision position against the elastic posterior capsule of the bag in which the posterior capsule is stretched rearward. After fibrosis is complete, natural brain-induced contraction and relaxation of the ciliary muscle relaxes and stretches the fused remnants and increases and reduces vitreous pressure in the eye, respectively, to effect vision accommodation by the fused remnants, the posterior capsule, and vitreous pressure.
However, prior art accommodating IOLs have certain drawbacks. For example, they do not address the problem of loss of accommodation in the eye. Accommodation may be lost during the aging process due to hardening of the natural lens. Loss of accommodation due to a progressive denaturation of the lens proteins produces an abnormal condition commonly known as “presbyopia”. Presbyopia generally affects individuals in the early to mid forties and the resultant gradual loss of visual acuity is generally treated with bifocal spectacles.
Accommodation may also be lost due to a change in the size of the lens, with a resultant loss in tension of the zonules, thereby affecting the ability of the zonules to focus the lens. This loss in accommodation may occur with aging, but may also occur upon removal of the natural lens. For example, in a normal human eye, the diameter of the crystalline lens may be approximately 8-9.5 mm, and may have an anterior-posterior thickness of approximately 4.5 mm. After removal of the cortex and nucleus of the lens, such as after phacoemulsification in cataract surgery, the capsular bag may extend to 10.5 mm and have a width of only 2.0 mm. This causes a slackening of the zonules, which is not restored by prior art apparatus or methods upon insertion of an IOL. Thus an IOL assembly that retains the accommodation ability of the eye, including the ability of the zonules to focus the lens, is greatly needed.